1. Field
Embodiments of the present invention relate to a master cylinder for brake systems which may improve brake feel.
2. Description of the Related Art
In a hydraulic brake system for vehicles, a master cylinder serves to generate hydraulic pressure and transfer the generated hydraulic pressure to a caliper brake installed at each wheel.
FIG. 1 shows a general tandem master cylinder. The master cylinder includes a first piston 3 and a second piston 4 installed in a bore 2 of a cylinder body 1 to be movable back and forth. The inside of the bore 2 is divided into a first hydraulic pressure chamber 5 and a second hydraulic pressure chamber 6 by the second piston 4. When the first piston 3 of the master cylinder moves forward, the first piston 3 applies pressure to the oil in the first hydraulic pressure chamber 5, and in turn the oil pressure in the first hydraulic pressure chamber 5 presses the second piston 4. Then, the second piston 4 applies pressure to the oil in the second hydraulic pressure chamber 6. Thereby, the oil in the first hydraulic pressure chamber 5 is supplied to the caliper brakes (not shown) of two wheels via a first oil discharge hole 7, and the oil in the second hydraulic pressure chamber 6 is supplied to the caliper brakes of the other two wheels via a second oil discharge hole 8.
The master cylinder is used for an F/R (front/rear) split-type vehicle or X-split (cross split)-type vehicle according to the brand or type of the vehicle. Here, the F/R-type split vehicle refers to a vehicle that controls hydraulic pressure supplied to the front wheels or the rear wheels, and the X-split-type vehicle refers to a vehicle which controls one of the front left wheel and the front right wheel and one of the rear left wheel and the rear right wheel. That is, the X-split-type vehicle controls the wheels in a cross manner that pairs one of the front wheels on one side with one of the rear wheels on the other side. The X-split type control is recently applied to a majority of vehicles since it allows one of the hydraulic chambers to produce braking pressure when the other hydraulic chamber malfunctions during braking operation, thereby securing driver safety.
Meanwhile, the caliper brake installed at each wheel serves to perform braking operation by pressing a disc rotating together with the wheel. However, if the caliper brake is arranged to increase the amount of rollback to reduce drag of the caliper which occurs during braking, an excessively large amount of hydraulic oil may be needed at the initial stage of braking, resulting in degradation of initial brake feel.
A structure to increase an initial flow rate, i.e., a structure to increase an initial flow rate in the first hydraulic pressure chamber, has been proposed to address the problems described above. However, this structure may cause pressure difference between the two hydraulic pressure chambers, resulting in difference in braking force among the wheels. Therefore, it may not be used for the X-split vehicle.